The present invention relates generally to the coupling of two electrical devices, and specifically to the coupling of integrated circuit chips to electronic cards using interconnections comprising conductive polymers.
Electrical components such as semiconductor devices and integrated circuit chips are, in general, mounted on a printed circuit board or “card” in order to be electrically connected with other electrical devices. The electrical connection from the first electrical component to the second electrical component is formed between external electrodes or contact pads on the first component to contact pads on the second component. The contact pads on each component are arranged to align with the matching contact pads on the other component.
Various methods for connecting the contact pads on the first component with the contact pads on the other component are known in the art, including use of ball grid arrays (BGAs), column grid arrays (CGAs), and land grid arrays (LGAs). For example, electrically conductive bonds that mechanically and electrically connect the first component and the second component at each pair of matching contact pads can be formed using solder balls. Solder balls are units of essentially sphere-shaped, solidified solder that have been applied to the contact pads of the first component. When all of the desired contact pads on the first component have had a solder ball applied, the component is said to comprise a “ball grid array”, or bump grid array. The ball grid array is placed so as to align each solder ball on the first component with the matching contact pads on the second component. FIG. 1a shows an electrical component with a ball grid array aligned over the substrate of a second component generally at 10. The first component 12 has a plurality of contact pads 14, onto each of which is affixed a solder ball 16. The second component substrate 18 has contact pads 20 aligned in a matching configuration to the first component contact pads 14.
FIG. 1b shows the configuration of the ball grid array after the solder balls 16 in the ball grid array have been placed in contact with the contact pads 20 on the second component substrate 18. Typically, the first component 12 is positioned in a parallel plane to the second component substrate 18, and a slight force is applied to the first component 12 to ensure contact between the entire ball grid array and the contact pads 20 on the second component substrate 18. The ball grid array is then heated, which causes the solder to reflow. The assembly is then allowed to cool. As shown in FIG. 1c, the final assembly comprises soldered interconnections 22 between the contact pads 14 of the first component 12 and the contact pads 20 of the second component substrate 18.
Conventional ball grid arrays, however, are not sufficiently resistant to interconnection breakage caused by differential expansion of the components. As the distance from the neutral point (where little or no interconnection stress occurs) of an interconnection increases, the reliability of that interconnection diminishes, because greater shear stresses are imparted on the interconnection.
Techniques have been developed to increase the distance between an electrical component and the substrate it is mounted on in order to provide for longer interconnections than can be achieved with a simple ball grid array. For example, multiple layers of solder balls or conductor layers can be used to increase the final distance between the component and the substrate (See, for example, U.S. Pat. No. 5,816,478 to Kaskoun and U.S. Pat. No. 5,641,113 to Somaki et al.). Although such lengthened interconnections are useful for larger substrates, the interconnections cannot be formed close enough to each other on a single substrate to allow use in many applications that require a higher density of interconnections on a component.
Interconnections formed through the various conventional techniques described above produce soldered connections that are prone to malfunction because the interconnections are relatively inflexible and therefore unable to withstand shearing forces created by the differing coefficients of thermal expansion of the materials in the components and interconnections.
What is needed in the art is an interconnection that allows for the ready incorporation of flexible and durable interconnections between the contact pads of two electrical devices.